1. Field of the Invention
The present invention relates to a contact type image sensor which reads an original from light reflected therefrom and can be used as an image pickup device of a facsimile, a copier, a scanner, and the like, and to an information processing apparatus using such a contact type image sensor.
2. Related Background Art
As an example of an original reader used with a facsimile, a copier, a scanner, or the like, a contact type image sensor is known which focusses an image of the original at a magnification factor of 1:1 and reads the image having the same size as the original with a sensor array. Such a contact type image sensor is constituted of: a sensor substrate formed with a plurality of sensor chips each having a plurality of pixels for photoelectric conversion and a protective film for protecting the sensor chips; a rod lens array for focussing an image of an original upon pixels of the sensor chips; and a cover glass defining an original reading surface, respectively mounted on a frame.
FIG. 15 is a schematic perspective view of a conventional contact type image sensor. Reference numeral 41 represents a frame for supporting the image sensor, and reference numeral 45 represents a transparent cover glass adapted to be in contact with an original and defining an original reading surface.
A plurality of optical sensors (pixels) are disposed along a longitudinal direction (main scan direction) DM of the frame 41, the shorter side direction DS being a sub-scan direction.
FIGS. 16A to 16C are cross sectional views showing the structures of different image sensors taken along line 17xe2x80x9417 in FIG. 15. Each image sensor shown in FIGS. 16A to 16C is constituted of: a light source 3 for illuminating an original; a rod lens array 2 disposed directly under an original reading surface of a cover glass 1; sensor chips 12; and a sensor substrate 18, respectively held in position by a frame 9. The image sensor shown in FIG. 16A has a bottom plate 8 integrally mounted on the frame 9 via a spacer 6. The image sensor shown in FIG. 16C has a transparent substrate 10 in place of the sensor substrate 18. In the image sensors shown in FIGS. 16A and 16B, a sensor array 19 is constituted of the sensor substrate 18 and sensor chips 12. A ceramic or glass epoxy substrate is used as the sensor substrate 18. After the sensor chips 12 are disposed on the substrate 18, wire bonding is performed to form the sensor array 19. The configuration of the frame 9 and the processing of the sensor substrate 18 have been determined so as to prevent stray light to be caused by external light and internally reflected light from entering sensor light reception areas. Other necessary components are also used for the image sensors shown in FIGS. 16A and 16B.
In the contact type image sensor shown in FIG. 16C, in place of the sensor substrate 18, the transparent substrate 10 such as a glass substrate with electrical wiring connections is used. The sensor array 19 is formed by mounting a plurality of face-down sensor chips 12 for photoelectric conversion in one line on the transparent substrate 10. High work precision of the image sensor has been set in order to prevent stray light to be caused by external light and internally reflected light from entering sensor light reception areas, more than the sensor arrays shown in FIGS. 16A and 16B.
FIG. 17 shows another example of the contact type image sensor shown in FIG. 15. A focussing unit 47 is disposed in a first space 41A of a frame 41. The focussing unit 47 has side plates 72 and 73 which allow a lens array of one or more lenses 71 to be disposed in rows. A light source 46 is disposed in a second space 41B. The light source 46 is constituted of: one or more LED light source units 63; a light guide plate 61 for guiding light from the light source along the main scan direction DM and illuminating an original PP; and a housing 62 for intercepting leak light from the light guide plate 61 and positioning the light guide plate 61 to efficiently illuminate the original PP.
The first and second spaces 41A and 41B communicate with each other. A sensor array 43 is mounted on an electrical circuit substrate 44 and is disposed between the frame 41 and a frame 42 as a second support, facing a third space 41C.
This image sensor is assembled in the following manner. The light source 46 is fixed to a mount plane 41D with adhesive or screws, and the focussing unit 47 is inserted into the first space 41A and fixed to a mount plane 41E with adhesive or screws.
The electric circuit substrate 44 with the sensor array 43 is fixed to the frame 41 by using the frame 42 or by using adhesive or screws.
With the above-described contact type image sensors, as shown in FIG. 18, in order to intercept a stray light beam 31 entering from a gap between a lens array and a frame, a stray light beam 32 entering from the bottom of each LED, and stray light beams entering from the sides and bottom of a sensor substrate, light interception walls are mounted on the frame, a gap is minimized with strict size precision, or other countermeasures are adopted. Therefore, components become complicated and bulky so that the assembly performance is degraded. Manufacture cost becomes high because of an increase in the number of components such as a bottom plate and an internal reflection preventing process.
In the case of a contact type image sensor such as shown in FIG. 16C which is formed by mounting a plurality of face-down sensor chips for photoelectric conversion in one line on a transparent substrate such as a glass substrate with electrical wiring connections, the merits of the transparent substrate become demerits because of entrance of stray light.
In order to further enhance and promote the compact structure and highest merit of the above-described contact image sensor, the following technical issues to be solved still exist.
(1) As the focussing unit 47 shown in FIG. 17 is made compact, the coating area of adhesive 49 for fixing the focussing unit 47 to the frame 41 becomes small. Therefore, it becomes difficult to coat the adhesive 49, or the adhesive may permeate into the surface of the focussing lens 71 to block the focussing optical path so that light information of the original PP into the sensor array 43 is intercepted to thus lower the image quality.
(2) If there is a variation in assembly works of inserting the focussing unit into the first space 41A and fixing it to the mount plane 41E, a position displacement of the focussing unit 47 from the mount plane 41E occurs so that the image quality is lowered.
An object of the present invention is to make compact a contact type image sensor. Another object of the invention is to improve an assembly performance of a contact type image sensor.
In order to achieve the above objects, according to one embodiment of the invention, there is provided a contact type image sensor comprising: a sensor substrate having photosensors mounted thereon; a focussing unit for focussing light from an original upon the photosensors; and a frame for holding the sensor substrate and the focussing unit, wherein the focussing unit abuts on the sensor substrate. With this embodiment, the contact type image sensor can be made compact.
According to another embodiment of the invention, there is provided a contact type image sensor comprising: photosensors; a support member for supporting an original; a focussing unit for focussing light from the original upon the photosensors; a frame for holding the photosensors, the focussing unit, and the transparent support member; and a focussing unit holding member disposed between the transparent support member and the focussing unit, for positioning the focussing unit relative to the frame. With this embodiment, the assembly works of the contact type image sensor become easy.
Other objects and aspects of the present invention will become apparent from the following detailed description of embodiments when read in conjunction with the accompanying drawings.